Thank you,RickHalle.
But my question isn't that.I sad hint window is the hint when I set the Hint property of the button and I set ShowHint := true.
Maybe you can tell me the message to show the hint.
thanks.

The catch is the active window part. You can fire the hint fairly easy using the Application.OnHint event and put it wherever you want. The problem I see is that the hint will not fire if the window is not active. I noticed the sample in the link I provided shows a hint window for the form even if it is not active. If you could instead get the hint for the control the cursor was over then you could show the hint for that control. (Instead of the xy coordinates) I know it is not a direct answer but it appeared that with a bit of work it could be coerced into working for buttons also. I played with it a little and was able to get it to pop up a hint window over the buttons by moving the form mousemove stuff to the button mousemove. When I did the window was flashing so it needed more work to find out why and then load the tip into it for the control(button).

Here is a modified unit for the sample code found at the above link that will display the button hint even if the window is not active. For Button1 you will need to add the mousemove event and set showhint to false.